Constructing cross-functional intumescent flame retardants with UV resistance for polypropylene composites

Cross-functional additives were carefully designed for polypropylene (PP) composites to enhance the flame retardancy, UV resistance, and mechanical properties. In this work, first, ammonium polyphosphate (APP) was coated with polysiloxane to avoid the pyrolysis of APP under UV irradiation; second, the charring formation agent (CFA) with triazine groups was selected to enhance the absorbance of UV radiation. Hindered amine light stabilizer (TEMP) was reacted with sodium lignin sulfonate (SLS) to obtain SLS-TEMP. By using 19 wt.% (SiAPP/CFA)/2 wt.% SLS-TEMP, the limiting oxygen index of the PP composite was increased to 33.5 and the UL-94 grade was achieved to V-0. The peak heat release rate and peak smoke release rate were reduced by 76% and 74% compared with that of the control PP sample, respectively. Moreover, the aging process of the PP composite sample was delayed. The tensile and impact strength of the PP/19 wt.%(SiAPP/CFA)/2 wt.%SLS-TEMP sample was decreased by 13.4% and 27.8%, respectively after 60 h UV irradiation, which was significantly lower than that of control PP (50.9% and 68%). The change of limiting oxygen index before and after aging was minimal, and the sample still passed UL-94 V-0 grade after 100 h UV-aging test. It was proved that the SLS-TEMP has an excellent synergy effect on improving the flame retardancy and UV resistance of PP. This cross-functional additive strategy provides a good solution for obtaining high-performance PP composites.